Magnetic transducer structure

ABSTRACT

A magnetic transducer structure is formed of a stack of individually shaped thin layers or films on a dielectric nonmagnetic substrate. The stack comprises near or at the outer surfaces thereof a pair of identically shaped magnetic layers spaced apart at an airgap end by portions of intervening insulating layers and contacting each other at the rear ends thereof. The intervening insulating layers together constitute a flat helix the turns of which surround the contacting portions of said magnetic layers and conductor layers in turn intervene between the insulating layers for developing a conductive flat helix embedded within the insulating helix. The turns of the insulating flat helix are registering and the turns of the conductor flat helix are registering. The insulating layers as well as the conductor layers are obtained by vapor deposition through a minimum number of perforated screens or masks which are repetitively used to form additional turns of the flat helices.

- United States Patent 1 Lazzari Nov. 5, 1974 .MAGNETIC TRANSDUCER STRUCTURE I 3,723,665 3/1973 Lazzari 179/1002 C [75] Inventor: Jean-Pierre Lazzari, Villiers Saint Primary Examiner Alfred H ddleman V F-tedenc France Attorney, Agent, or Firm-Kemon, Palmer & [73] Assigneei Compagnie Internationale Pour Estabrook LInformatique, Louv'eciennes, France [57] ABSTRACT [22] Filed: e 25 1973 A magnetic transducer structure is formed of a stack of individually shaped thin layers or films on a dielec- 1 PP 4 373,460 tric non-magnetic substrate. The stack comprises near or at the outer surfaces thereof a pair of identically [30] Foreign Application Priority Data shaped magnetic layers spaced apart at an airgap end J l 3 1972 F I 72 23939 by portions of intervening insulating layers and conu y rance tacting each other at the rear ends thereof. The intervening insulating layers together constitute a flat helix 8 gf g? g the turns of which surround the contacting portions of [58] d h l79/l00 2 340/l74 1 F, said magnetic layers and conductor layers in turn ins 0 23 360/l'2l 3 tervene between the insulating layers for developing a conductive flat helix embedded within the insulating helix. The turns of the insulating flat helix are register- [56] References cued ing and the turns of the conductor flat helix are regis- UNITED STATES PATENTS tering. The insulating layers as well as the conductor 3,344,237 9/1967 Gregg 179/ 100.2 C layers are obtained by vapor deposition through 21 3,549,825 12/1970 Trimble 179/1002 C minimum number of perforated screens ()1- masks 3,564,558 2/197l Tlman et a1 179/1002 C which are repetitively used to form additional turns of 3,611,417 [0/1971 Sauter et a1 179/1002 C the flat helices 3,639,699 2/1972 Tiemann 179/1002 C 10/1972 Nagao 179/ 100.2 C 6 Claims, 5 Drawing Figures PAINIEUNuv 51914 Fig. 3

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1 MAGNETIC TRANSDUCER STRUCTURE THE PRIOR ART of magnetic material, spaced apart at their airgap face end portions and contacting one another at their opposite end portionslntervening insulating and conductive layers define a flat induction coil the turns of which" pass around the contacting portions of the magnetic layers and part of the turns have converging portions at or near the airgap end portions of the magnetic layers, but the turns usually spread over the surface of the substrate around the" said magnetic layers. Such a coil arrangement unduly increases the electrical path so that, for a recording operation at least, the temperatureof the coil rise unduly. It has been suggested to tentatively restrict the overall area covered by the stack over the substrate, by making some turns in overlapping relation with some other ones, of different widths. Usually the width of the turns decreases from the turn layer contacting the substrate to the top layer of the coil. Additionally in view of the electrical efficiency unbalance from turn to turn, it must be noted that one consequence of such an arrangement is that it necessitates as many masks for deposition of the layers (usually a complete turn per layer) as there are layers. Consequently, the number of turns of a transducer to be manufactured must be strictly pre-determined. No increase in the number of turns can be made without further increasing the area occupied'by the coil on the substrate and each such increase necessitates the use of to an additional mask.

THE OBJECTS THIS THE INVENTION It is an object of the invention to provide a magnetic transducer structure of the integrated circuit technique kind which avoids the above drawbacks.

It is a further object of the invention to provide a magnetic transducer structure which may be formed with any number of coil turns with a minimum number of deposition masks.

It is a further object of the invention to provide such a magnetic transducer structure which may be formed, with such a reduced number of deposition masks, having its coil wound in either one of the two possible directions and even in both directions at distinct levels thereof.

It is a further object of the invention to provide a magnetic transducer structure such that it may include intermediate taps on its coil.

BRIEF SUMMARY OF THE INVENTION A magnetic transducer structure according to the invention optimizes the above analysed prior art structures in that it's coil comprises a plurality of insulating layers together constituting a flat insulating helix the turns of which surround the contacting portions of its pair of magnetic layers and portions of which intervene between the spaced apart airgap ends of said pair of magnetic layers. Conductor layers intervene between the layers of the insulating helix and form a conductive flat helix embedded therein with the exception of rear terminal portions, the turns of the said insulating helix being in substantially mutual registration and the turns of the said conductive helix being in substantially mutual registration. Each one of the insulating and conductive layers in the said helices have an axis of symmetry coincident with the front-to-rear axis of symmetry of the said pair of magnetic layers or being a mirror image of another one of the layers with respect to the said axis of symmetry of the said pair of magnetic layers.

Such a magnetic transducer structure comprises, as a minimal stack on a dielectric non-magnetic substrate:

a. a first magnetic layer one edge of which substantially registers with the front edge of the substrate, extending over predetermined length towards the rear edge of said substrate and havingan axis of symmetry along the said front-to-rear direction,

b. a first insulating U-shaped layer the transverse branch of which substantially registers with the front edge portion of the said first magnetic layer and the legs of which, encompass the said first magnetic layer in close proximity thereto, each extending toward the rear edge of the substrate over a longer length than the rear extension of said first magnetic layer,

c. a first conductive U-shaped layer, the transverse branch and legs of which are of smaller widths than those of the layer b) over which they apply, one leg of which extends substantially up to the rear edge of the substrate and the other leg of which extends beyond the length of the legs of the layer b), d. a second insulating layer repeating the layer b), e. a third insulating layer of asymmetrical shape with respect to the axis of symmetry of the magnetic layer a), masking the longer leg of the conductive layer c) up to a distance from the rear edge of the substrate shorter than the distance between said rear edge and the other leg of the layer c),

f. a transverse conductive layer contacting the exposed part of the layer c) and symmetrically extending with respect to the axis of symmetry of the layer a),

g. a fourth insulating layer, the mirror image of the layer e) with respect to the axis of symmetry of the .of the following sequence of layers:

1. a U-shaped conductive layer the transverse branch 1 of which repeats the transverse branch of the layer c) and the legs of which each repeats the shorter leg of c),

m. an insulating layer repeating the layer b),

n. an insulating layer repeating the layer e),

o. a conductive layer repeating the layer f), and,

p. an insulating layer repeating the layer g).

For constructing an intermediate tap on the coil, an additional conductive layer q) is inserted either just before or just after a layer such as f) or 0), said additional from the position of such a layer f) or The winding direction of the coil may be reversed by permutation of the layers e) and g) and of the layers c) and h). A reversal of progression of the turns may be provided from one turn to the next one by permutating the layers n) and p) in an additional sequence.

Such reversals of the direction of progression of the turns are mainly useful for a modification of the structure wherein at least one complete turn is provided between the substrate and the first magnetic layer and one complete turn of the coil is provided over the sec- 4 0nd magnetic layer. The external turns may advantageously be provided with a direction of progression opposite to the direction of progression of the internal turns between the magnetic layers. The first external turn from the substrate begins with a layer c) and the last external turn of the coil ends with a layer h), the magnetic layers a) and k) intervening each after a layer b) in the stack.

Analysis of the above defined structures demonstrates that, in structures according to the invention, only one shape of magnetic layer, three shapes of insulating layers and five shapes of conductive layers are necessary. Consequently, when such structures are made a conventional deposition process within a vacuum vessel, only nine perforated screens are necessary. A single mask bearing such perforations may be introduced in the vessel and, from appropriately programmed sequences of translations simultaneous with programmed sequences of activations of source materials within said vessel, complete structures may be made without necessity of breaking the vacuum of the vessel. I

BRIEF DESCRIPTION OF THE DRAWINGS For the sake of simplicity, only one example of the invention is illustrated by the attached drawings:-

FIGS. 1 and 2 respectively show a top view ofa transducer structure and an equivalent electrical circuit of the coil thereof,

FIG. 3 shows a mask provided with the nine perforated areas useful for obtaining the structure of FIGS. 1 and 2.

FIGS. 4 and 5, respectively oriented along perpendicular planes, one of which coincides with the axis of symmetry of the structure, show exploded side elevations of the transducer structure. For the sake of simplicity, the actual shapes of the layers when formed one over another are neglected and all layers are shown in a planar representation thereof.

A magnetic transducer structure according to the invention is essentially intended to be obtained by successively evaporating layers of materials on a substrate within a vacuum vessel, in a continuous process avoiding any break of the vacuum during the entire formation of the structure. This can be done with a perforated screen or mask (50), FIG. 3, having nine perforated areas, numbered from (1) to (9), each areas being of the same height and the same width. These areas may be aligned as shown so that, once the mask is mounted within the vessel in a plane parallel to the plane of the substrate 10, it may be controlled by stepped translations to position each area between the source and the substrate on which the stack of the transducer structure must be formed. Stepping translation mechanisms within vacuum vessels are known in the art. Preferably, a screen 51, having an aperture de- Iineating the useful area of the substrate is placed between the mask and the substrate. Evaporatable material sources are arranged on the outer face of the mask according to any known arrangement ensuring a uniform coverage of the receiving surface of the substrate by the evaporated materials. Such sources are indicated at 52, 53 and 54, as three materials which must be evaporated, i.e., magnetic, insulating and conductive. At each positioning of the mask with respect to the substrate, one of such sources is activated by heating the .pellets which constitute the source.

Each evaporated layer will have the shape and the position defined by the corresponding perforation of that area of the mask through which it has been deposited onto the substrate 10. At area (1) of the mask, the perforation (m) defines the shape of a magnetic layer, or pole-piece, of the structure such as 11 and 12, FIGS. 2 and 4-5. This perforation (m) has an edge at the level of the upper side of the area (1) and an axis of symmetry coinciding with the axis of symmetry of the area in the direction of the height thereof. The layers '11 and 12 will consequently have an edge coinciding with the front edge (or airgap" edge) of the substrate. The areas (3), (4) and (6) of the mask (50) are perforated for defining the shapes and positions of the insulating layers used in the stack. The perforation (3) is U-shaped and the perforations (4) and (6) are mirror images with respect to the axis of symmetry of the areas. When superimposed, the perforations together define a rectangular zone having a central rectangular hole in which end portions of the magnetic layers 11 and 12 will be in contact. At the formation of the structure, the layers 11 and 12 will extend slightly beyond the front edge of the insulating layer (3). Thereafter, as later described, the front edges of the magnetic and insulating layers (3) will be made level at the airgap face. The perforations ofthe areas (2), (5), (7), (8) and (9) through which the conductive layers are evaporated define, when superimposed, a single turn coil having rear input, output and mid-point tap branches extending up to the rear edge of the substrate. Omission of the layer (8) eliminates the midpoint tap. The combined effect of evaporating through the (d) and the (c) perforations (d) for dielectric, (c) for conductive result in a flat helix of electrically interconnected conductive segments which are relatively insulated and actually embedded within a corresponding flat helix of insulating, or dielectric, material segments. The width of the conductive segments is slightly less than the width of the insulating segments. Illustratively, a single turn coil without mid-tap output may be made by evaporating material onto a substrate using the following sequence of areas ofthe mask 50:- (2) (3) (4) (5) (6) (7) (3) (4) (6) (9) and the magnetic transducer'structure may be completed by providing a magnetic layer on each face of such a coil. The turns of the coil close near the airgap edges of the magnetic layers and extend close to the side and rear edges of the magnetic layers, and said turns register in the development of the helix coil, so that, finally, the developed length of the coil is optimized for high efficiency of the transducer.

The various layers and their overlapping zones are shown in a top view in FIG. 1 full lines for the magnetic and conductive layers, interrupted lines for the insulating layers. An illustrative coil circuit is shown in FIG. 2 and FIGS. 4 and 5 show in exploded views, as

hereinabove defined, a stack the coil of which conforms to the circuit of FIG. 2.

The substrate first receives a magnetic layer 11 through the perforation of the area (1) of the mask (50), magnetic material source 52 being activated during the time area (1) faces the substrate. Thereafter, from a two step translation of the mask 50, the area (3) is positioned between the source and the substrate and the insulator material source 53 is then activated.

This operation results in the formation of an insulating layer 31 the transverse branch of which passes over the fore part of the magnetic layer 11, said layer 31 extending symmetrically on both sides of the layer 11. As the coil of the example turns in a clockwise direction, it is thereafter a conductive layer 2 which is provided through the perforation of the area (2) of the mask 50 over the insulating layer 31. The left-hand leg of the conductive layer 2 reaches the rear edge of the substrate and its right-hand branch extends beyond the corresponding leg of the layer 31. Right and left are defined with respect to FIG. 3. Clockwise and anticlockwise directionsare defined with respect to FIG. 2. Source54 is activated each time a conductive layer is coated in the stack of layers on the substrate. Thereafter, the area (3) of mask 50 is again positioned between the source and the substrate for deposition of a second insulating layer 32 identical to layer 31, the rear parts of the legs of the conductive layer 2 are exposed. Over the longer leg of layer 2 is coated an insulating layer 41 through the perforation of the area (4) of mask 50 and then a conductive layer 510 is coated through the perforation of the area (5) of mask 50. The conductive layer 510 is insulated from theleft-hand leg of 2 but contacts the right-hand leg of 2. An insulating layer 61 is formed through the perforation of the area (6) of the mask so that said layer 61 coats the right-hand portion of the conductive layer 510 leaving exposed the lefthand portion thereof. A conductive layer 71 is formed through the perforation of the area (7) of the mask, its left hand leg contacting the layer 510. Insulating layers 33 and 42 are successively formed and a further conductive layer 520 is coated over the stack for further development of the circuit of the coil. It is assumed that an intermediate tap must be provided in the coil so that a layer 8 is formed through the perforation of the area (8) of the mask, said layer contacting the layer 520 and extending to the rear edge of the substrate 10. The development of the coil goes on through the successive formations of the insulating layer 62, conductive layer 72, insulating layers 34 and 43, conductive layer 530 and insulating layer 63. The coil is terminated with a conductive layer 9 which is the mirror image of the layer 2 with respect to the front-to-rear axis of symmetry of the structure and is formed through the perforation of the area (9) of the mask. Finally, a further insulating layer 35 is coated over the stack and over said layer 35 is formed the magnetic pole-piece layer 12.

Though the various layers are shown in flat form in the exploded views of FIGS. 4 and 5, it is obvious that, intheir contacting relations on the substrate, each layer will vary in thickness depending on the varied level surface defined by the preceding layers of the stack from the planar substrate face. When a planar external surface for the structure is desired, a protective dielectric material may be provided, as indicated by the interrupted line 55 in FIGS. 4 and 5.

For an anticlockwise direction of the turns of the coil, the sequence of deposition of the layers will be:- 11-31-9-32-61-510-41-71-33-62-520-9 -42-72-34-63-530-43-2-35-12.

Once the structure is completed and extracted from the vessel, its left-hand part, as shown in FIGS. 1 and 4, is removed by abrading it for instance up to the line 56. This operation exposes the airgap constituted by the two edges of the magnetic layers 11 and 12 with the intervening edges of the insulating layers 31 to 35 which, at this place, contact each other in the stack. Of course, such an operation may be unnecessary or necessary only to a lesser extent, when the layers 3 are provided with front edges directly aligned with the front edge of the substrate.

A modification of the sequence of the layers the order of occurrences of the layers (3) and (4), or (3) and (6) as the case may be, is reversed after any formation of a layer (7) in the stack.

Minor variations may obviously be brought in the shapes of the layers without altering the gist of the invention.

It is further obvious that a plurality of magnetic transducers may be simulataneously formed at spaced areas of a single substrate, the row of perforation locations of the screen, or mask, 50 being duplicated as many time as the number of transducers which are to be provided on the substrate.

The magnetic material (m) may be an iron-nickel alloy the components of which are simultaneously evaporated from separate pellets the rates of evaporation of which are adjusted, as known in the art, to produce a desired iron/nickel ratio in the layers. The conductive material may be copper. The insulating material may be silica obtained, as known, from evaporation of SiO within a low pressure atmosphere of oxygen or water vapour. The substrate 10 may be a high melting point glass.

By way of example, a coil presenting two internal reversals of the direction of progression of turns, having one external turn each side of the magnetic airgap, may be as follows:

Other modifications will be obvious to those skilled in this art.

What is claimed is:

l. A magnetic transducer structure formed of a stack of individually shaped thin layers coated on a dielectric non-magnetic substrate having substantially parallel front and rear edges, the stack comprising a pair of magnetic layers having a front to rear axis of symmetry with respect to the substrate, spaced apart at one end to define an air-gap face end portion adjacent one edge of said substrate and contacting one another at their opposite end portions at a point between the front and rear edges of said substrate, and a flat helix insulated conductor coil at least a part of which surrounds the contacting portions of said magnetic layers wherein a plurality of insulating layers of the stack together define a flat insulating helix having portions of its turns surrounding said contacting portions of said magnetic layers and having portions of its turns positioned between the magnetic layers at the airgap faces thereof, wherein conductive layers of smaller dimensions in the plane parallel to said substrate are positioned between said insulating layers to define a conductive flat helix embedded within the insulating helix with the exception of rear terminal portions which extend substantially to the rear edge of said substrate, wherein the turns of the insulating helix are in substantially mutual registration and the turns of the conductive helix are also in substantially mutual registration and wherein each one of said insulating and conductive layers in the helixes either has an axis of symmetry coincident with the said front to rear axis of symmetry of the pair of magnetic layers or is a mirror image of another one of the layers with respect to said front to rear axis of symmetry.

2. A magnetic transducer structure as defined by claim 1 comprising the following minimal stack of layers on said substrate;

a. a first magnetic layer, one edge thereof substantially registering with the front edge of the sub strate and which extends over a pre-determined length towards the rear edge of said substrate with an axis of symmetry coincident with the front to rear direction of said substrate;

b. a first insulating U-shaped layer the transverse branch of which substantially registers with said front edge of said substrate and layer (a) and the legs of which surround said layer (a) in close proximity thereto, each extending towards the rear edge of said substrate over a greater length than that of layer (a);

c. a first U-shaped conductive layer, the transverse branch and legs of which are of smaller widths than v those of layer (b) over which they are applied, one leg extending substantially up to the rear edge of said substrate and its other leg extending beyond the length of the legs of layer (b);

d. a second insulating layer identical to layer (b);

e. a third insulating layer of asymmetrical shape with respect tothe axis of symmetry of layer (a), masking the longer leg of layer (c) up to a distance from the rear edge of said substrate less than the distance of said rear edge to the other leg of layer (c);

f. a transverse conductive layer contacting the exposed part of the shorter leg of layer (c) and symmetrically extending with respect to the axis of symmetry of layer (a);

g. a fourth insulating layer, which is a mirror image of layer (a) with respect to the axis of symmetry of layer (a);

h. a third conductive layer which is a mirror image of layer (0) with respect to the axis of symmetry of layer (a);

j. a fifth insulating layer identical to layer (b);

k. a second magnetic layer identical to layer (a); Such structure further comprising, respectively, for each additional coil turn, an insertion after layer (g), said insertion being:

1. a U-shaped conductive layer the transverse branch of which is identical to the transverse branch of layer (0) and the legs of which are identical tothe shorter leg of layer (0);

Y m. an insulating layer identical to layer (b);

n. an insulating layer identical to layer (e);

o. a conductive layer identical to layer (f); and

p. an insulating layer identical to layer (g).

3. A magnetic transducer structure according to claim 2, further comprising, for each intermediate tap of the coil;

q. a conductive layer extending substantially up to the rear edge of the substrate from a distance from said rear edge enabling contact with a layer f) and inserted prior or after such a layer f) in the stack.

4. A magnetic transducer structure according to claim 2, wherein the occurrences of the layers d) and e), respectively the occurrences of the layers m) and h), are permutated in the stack.

5. A magnetic transducer structure according to claim 2, wherein the layers n)-and p) are permutated in each turn requesting a reversal of its direction of progression with respect to the next preceding one in the stack.

6. A magnetic transducer structure according to claim 2, wherein, prior the layer a), respectively after the layer k), the stack includes at least one additional turn as per the sequence of layers 1) to p), the layers n) and p) in such sequences being permutated with respect to their order of occurrence in the turns established in the stack between the layers a) and k). 

1. A magnetic transducer structure formed of a stack of individually shaped thin layers coated on a dielectric nonmagnetic substrate having substantially parallel front and rear edges, the stack comprising a pair of magnetic layers having a front to rear axis of symmetry with respect to the substrate, spaced apart at one end to define an air-gap face end portion adjacent one edge of said substrate and contacting one another at their opposite end portions at a point between the front and rear edges of said substrate, and a flat helix insulated conductor coil at least a part of which surrounds the contacting portions of said magnetic layers wherein a plurality of insulating layers of the stack together define a flat insulating helix having portions of its turns surrounding said contacting portions of said magnetic layers and having portions of its turns positioned between the magnetic layers at the airgap faces thereof, wherein conductive layers of smaller dimensions in the plane parallel to said substrate are positioned between said insulating layers to define a conductive flat helix embedded within the insulating helix with the exception of rear terminal portions which extend substantially to the rear edge of said substrate, wherein the turns of the insulating helix are in substantially mutual registration and the turns of the conductive helix are also in substantially mutual registration and wherein each one of said insulating and conductive layers in the helixes either has an axis of symmetry coincident with the said front to rear axis of symmetry of the pair of magnetic layers or is a mirror image of another one of the layers with respect to said front to rear axis of symmetry.
 2. A magnetic transducer structure as defined by claim 1 comprising the following minimal stack of layers on said substrate; a. a first magnetic layer, one edge thereof substantially registering with the front edge of the substrate and which extends over a pre-determined length towards the rear edge of said substrate with an axis of symmetry coincident with the front to rear direction of said substrate; b. a first insulating U-shaped layer the transverse branch of which substantially registers with said front edge of said substrate and layer (a) and the legs of which surround said layer (a) in close proximity thereto, each extending towards the rear edge of said substrate over a greater length than that of layer (a); c. a first U-shaped conductive layer, the transverse branch and legs of which are of smaller widths than those of layer (b) over which they are applied, one leg extending substantially up to the rear edge of said substrate and its other leg extending beyond the length of the legs of layer (b); d. a Second insulating layer identical to layer (b); e. a third insulating layer of asymmetrical shape with respect to the axis of symmetry of layer (a), masking the longer leg of layer (c) up to a distance from the rear edge of said substrate less than the distance of said rear edge to the other leg of layer (c); f. a transverse conductive layer contacting the exposed part of the shorter leg of layer (c) and symmetrically extending with respect to the axis of symmetry of layer (a); g. a fourth insulating layer, which is a mirror image of layer (a) with respect to the axis of symmetry of layer (a); h. a third conductive layer which is a mirror image of layer (c) with respect to the axis of symmetry of layer (a); j. a fifth insulating layer identical to layer (b); k. a second magnetic layer identical to layer (a); Such structure further comprising, respectively, for each additional coil turn, an insertion after layer (g), said insertion being:
 3. A magnetic transducer structure according to claim 2, further comprising, for each intermediate tap of the coil; q. a conductive layer extending substantially up to the rear edge of the substrate from a distance from said rear edge enabling contact with a layer f) and inserted prior or after such a layer f) in the stack.
 4. A magnetic transducer structure according to claim 2, wherein the occurrences of the layers d) and e), respectively the occurrences of the layers m) and h), are permutated in the stack.
 5. A magnetic transducer structure according to claim 2, wherein the layers n) and p) are permutated in each turn requesting a reversal of its direction of progression with respect to the next preceding one in the stack.
 6. A magnetic transducer structure according to claim 2, wherein, prior the layer a), respectively after the layer k), the stack includes at least one additional turn as per the sequence of layers 1) to p), the layers n) and p) in such sequences being permutated with respect to their order of occurrence in the turns established in the stack between the layers a) and k). 